The present invention concerns the field of freewheel devices used in automatic transmissions for motor vehicles, for example.
Freewheel devices generally comprise an outer ring with a cylindrical inner sliding path for cams of the freewheel, an inner ring or a shaft having a cylindrical outer sliding path for said cams of the freewheel, a freewheel between the sliding path of the outer ring and the sliding path of the inner ring or the shaft, and one or more bearing members for holding the inner and outer rings concentric and transmitting radial forces between said rings.
A bearing is a generally annular component having a radial part in the form of a substantially plane washer delimited by two circular edges to each of which an axial portion is joined. The axial portions bear on corresponding bearing surfaces of the rings, so centering the two rings relative to each other in the manner of smooth bearings. Said corresponding bearing surfaces of the rings can be an axial extension of the corresponding sliding paths.
The freewheel comprises a single cage or a double cage comprising two concentric cages with windows containing cams which, by becoming wedged between or sliding between the two sliding paths, assure unidirectional coupling between the inner and outer rings. The freewheel is able to transmit torque in one direction between the inner and outer rings and allows free rotation in the other direction.
To encourage tilting of the cams in the wedging direction a spring can be provided in the form of a strip applying to each cam a return torque urging it at all times into contact with the sliding paths.
The various components of the freewheel device can move relative to each other, rings relative to cams, cages relative to bearings, rings relative to bearings, or relative to adjoining components such as friction discs, retaining flanges, etc.
It is therefore necessary to lubricate these components to encourage sliding and to evacuate heat generated by friction.
Prior art documents, and in particular documents U.S. Pat. No. 4,875,564 and JP-A-326 866, describe lateral smooth bearings in freewheels and having in the middle of their disc-shape radial part lubricating holes through which the lubricant can be evacuated, which lubricant is generally injected under pressure into the assembly by means of a passage opening onto the path of the inner ring or the shaft.
This arrangement has certain drawbacks, however. Because the parts rotate, the lubricant tends to be centrifuged towards the outside of the sliding path on the outer ring. There is a volume radially between the lubricating holes of the bearings and the path of the outer ring in which the lubricant tends to stagnate with the result that it is not renewed or is not renewed properly. The lubricant circulates badly, heat is evacuated imperfectly and localized heating occurs in this area, which can further aggravate the phenomenon if the bearings are made of copper alloy.
The coefficient of thermal expansion of a copper alloy is higher than that of the steel constituting the other parts and in particular the rings. The bearings tend to bind on the outer ring and the small radial clearance between the bearing and the outer ring becomes insufficient to allow circulation of the lubricant. The phenomenon of stagnation of the lubricant is therefore aggravated and there is an increased risk of binding between the outside cylindrical bearing surfaces of the bearings and the corresponding bearing surface of the outer ring.